That makes sense to me 
If the spell instructions didn’t mention that part, then I’d wait until you are no longer seeing lights around the jar and then bring it far away (similar to what you would do with disposing spell remains) and then let them free on the condition that they don’t come back to bother you.
Although I love learning about them, I don’t work with any Fae and can’t give any personal advice about working with them. But I know that many folklores and legends warn about making deals or agreements of any kind with the Fae. So if you take this option, I’d recommend going about it carefully.
Blessed be! 